A method for establishing a biomimetic vertical axis wind turbine model

Abstract

This invention discloses a method for establishing a biomimetic vertical axis wind turbine model. It relates to a model establishment method. This invention aims to address the problem of low power generation efficiency in existing vertical axis wind turbines due to blade limitations. The steps of this invention include: Step 1, selecting the NACA0021 airfoil as the blade profile; Step 2, the shape of the leading edge protrusion of the wind turbine blade is a sine curve, and the convex peak cross-section profile is obtained by transforming the basic airfoil; Step 3, dividing the computational domain into an external fixed domain and an internal rotating domain; Step 4, calculating the wind turbine flow field using ANSYS Fluent software; Step 5, verifying the accuracy of the numerical simulation of the vertical axis wind turbine. This invention belongs to the technical field of biomimetic vertical axis wind turbines.

Description

Technical Field

[0001] This invention relates to a model building method, belonging to the field of biomimetic vertical axis wind turbine technology. Background Technology

[0002] Due to the increasing depletion of non-renewable resources such as oil and coal, and the serious environmental pollution caused by fossil fuel power generation, more and more countries are investing a lot of manpower and funds in the research and application of renewable resources. Wind energy is a low-cost, clean, environmentally friendly, convenient, and inexhaustible energy source, and is the most promising renewable resource for development and utilization in the near future.

[0003] Currently, wind turbine generators mainly include horizontal axis wind turbines and vertical axis wind turbines. Compared with horizontal axis wind turbines, vertical axis wind turbines are characterized by their rotating axis being perpendicular to the ground, the rotor's rotation plane being parallel to the wind direction, and the force direction remaining constant during rotation. They do not require an upwind adjustment system, resulting in higher reliability and a longer fatigue life than horizontal axis generators. Furthermore, vertical axis wind turbines can be placed far below the rotor or even on the ground, facilitating installation and maintenance.

[0004] The Darrieux-type wind turbine is a vertical axis wind turbine, mainly composed of rotor blades, a gearbox, a generator, cables, and top and bottom rotor centers. The upper part of the blades is connected to the top rotor center, and the lower part is connected to the bottom rotor center. The rotation of the rotor blades drives the vertical axis to rotate, and the shaft transmits power to the generator after being geared by the gearbox, thus achieving the function of generating electricity. Because the horizontal radius of the rotor blades is large and the shaft is relatively high, cables are used to fix it to the ground from the top to address the strength issues caused by the large wind forces during rotation, which to some extent wastes space. Furthermore, the main tower support bearings need to withstand huge radial and axial loads, and vertical vibrations also generate a series of alternating loads. In addition, if the power generation equipment malfunctions, maintenance and repair are relatively troublesome, resulting in long lead times and low efficiency.

[0005] Currently, this type of vertical axis wind turbine is mature and has advantages such as simple structure and low cost. However, the biggest problem is that the power generation efficiency is low due to the structural limitations of the blades, especially for high-power generator sets, where there are great limitations on materials and structural costs. Summary of the Invention

[0006] This invention addresses the problem of low power generation efficiency in existing vertical axis wind turbines due to blade limitations, and proposes a biomimetic method for establishing a vertical axis wind turbine model.

[0007] The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the present invention include:

[0008] Step 1: Select the NACA0021 airfoil as the blade profile;

[0009] Step 2: The shape of the leading edge protrusion of the wind turbine blade is a sine curve, and the profile of the convex peak section is obtained by transforming the basic airfoil;

[0010] Step 3: Divide the computational domain into a fixed domain on the outside and a rotated domain on the inside;

[0011] Step 4: Calculate the wind turbine flow field using ANSYS Fluent software;

[0012] Step 5: Verify the accuracy of the numerical simulation of the vertical axis wind turbine.

[0013] Furthermore, in step 1, the blade chord length of the blade profile is c = 0.265m, the blade height is H = 1.2m, and the blade rotation radius is R = 1m.

[0014] Furthermore, the transformation method for the convex peak cross-sectional profile is as follows:

[0015]

[0016] In formula (1), (x k y k ) represents the coordinates of the point with the maximum thickness of the airfoil, and A represents the amplitude of the bulge.

[0017] Furthermore, in step 3, the rotation radius of the rotating domain is 1.2R, the height of the rotating domain is the same as the blade height, which is H, the left entrance of the fixed domain is a semicircle with a radius of 10R, and the outlet of the fixed domain is 30R away from the rotating domain. In order to consider the influence of tip vortex generation in the study, the domain height is calculated to be greater than the blade height, and is set to 2H.

[0018] Furthermore, in step 4, the turbulence model adopted is the k–ωSST model, which is widely used in numerical simulations of vertical axis wind turbines. Incompressible air is selected as the flow medium, and the fluid density is set to 1.225 kg / m³. 3 The calculation time step is set to the time required for the blade to rotate 1°, with 40 iterations in each time step, and the total physical calculation time is set to the time required for the wind turbine blade to rotate 16 times.

[0019] Furthermore, in step 5, the time step, total physical duration, mesh density, and differences between simulation and experiment are verified. The relationship between the power coefficient, torque coefficient, and tangential force coefficient is as follows:

[0020]

[0021] In formulas (2), (3), and (4), C powerThe wind turbine power coefficient is TSR, tip speed ratio is Q, wind turbine torque is ρ, gas density is H, wind turbine blade height is R, blade rotation radius is U, and mainstream velocity is C. Q It is the torque coefficient of the wind turbine, C T is the tangential force coefficient of the wind turbine, and c is the average chord length of the blade.

[0022] The beneficial effects of this invention are as follows: This invention addresses the problem of low power coefficient of vertical axis wind turbine blades by using a passive control method of biomimetic leading-edge protrusions to improve performance; at the optimal tip speed ratio, the biomimetic blade can improve the performance of vertical axis wind turbines by up to 6.28%; the biomimetic protrusions form counter-rotating flow vortices at the leading edge of the blade, which have an upwashing or downwashing effect on the airflow in the middle of the vortex; the biomimetic blade will withstand greater tangential forces from spanwise unevenness and the combined force of the main shaft. Attached Figure Description

[0023] Figure 1 This is a simplified schematic diagram of a biomimetic vertical axis wind turbine model;

[0024] Figure 2 This is a schematic diagram of the transformation process of the convex peak profile;

[0025] Figure 3 This is a schematic diagram of the computational domain model and boundary conditions;

[0026] Figure 4 This is a schematic diagram of the computational domain mesh partitioning;

[0027] Figure 5 This is a schematic diagram illustrating the determination of total computation time and time step.

[0028] Figure 6 This is a schematic diagram of the grid node distribution and grid density. Detailed Implementation

[0029] Specific implementation method one: as follows Figures 1 to 6 As shown, a method for establishing a biomimetic vertical axis wind turbine model includes the following specific steps:

[0030] Step 1: Select the NACA0021 airfoil as the blade profile; the blade chord length of the blade profile is c = 0.265m, the blade height is H = 1.2m, and the blade rotation radius is R = 1m;

[0031] Step 2: The shape of the leading edge protrusion of the wind turbine blade is a sine curve, and the profile of the convex peak section is obtained by transforming the basic airfoil; the transformation method of the convex peak section profile is as follows:

[0032]

[0033] In formula (1), (x k yk ) represents the coordinates of the point where the airfoil has the maximum thickness, and A represents the amplitude of the bulge;

[0034] Step 3: Divide the computational domain into an external fixed domain and an internal rotating domain; the rotation radius of the rotating domain is 1.2R, and the height of the rotating domain is the same as the blade height, which is H. The left entrance of the fixed domain is a semicircle with a radius of 10R, and the outlet of the fixed domain is 30R away from the rotating domain. In order to consider the influence of tip vortex generation in the study, the height of the computational domain is greater than the blade height and is set to 2H.

[0035] Step 4: Calculate the flow field of the wind turbine using ANSYS Fluent software; the k–ωSST model, widely used in numerical simulations of vertical axis wind turbines, is employed as the turbulence model. Incompressible air is selected as the flow medium, and the fluid density is set to 1.225 kg / m³. 3 The calculation time step is set to the time required for the blade to rotate 1°, and 40 iterations are set in each time step. The total physical calculation time is set to the time required for the wind turbine blade to rotate 16 times.

[0036] Step 5: Verify the accuracy of the numerical simulation of the vertical axis wind turbine; examine the time step, total physical duration, mesh density, and differences between simulation and experiment. The relationship between the power coefficient, torque coefficient, and tangential force coefficient is as follows:

[0037]

[0038] In formulas (2), (3), and (4), C power The wind turbine power coefficient is TSR, tip speed ratio is Q, wind turbine torque is ρ, gas density is H, wind turbine blade height is R, blade rotation radius is U, and mainstream velocity is C. Q It is the torque coefficient of the wind turbine, C T It is the tangential force coefficient of the wind turbine. It is the average chord length of the blade.

[0039] The average chord length of the blades is shown in the table below:

[0040] Table 6-1 Average chord length of blade

[0041]

[0042] The prototype blade is named O blade. The blade with a convex amplitude of A = 0.025c = a0 = 0.006625m and a wavelength of W = H / 3 = w0 = 0.4m is defined as the reference blade W(A) blade. The subscripts of W series and A series mean that the convex wavelength or amplitude is a multiple of the corresponding value of the reference blade. The convex amplitude of WN series is w0. The subscript of W means the same as above. The subscript of N means the number of convex protrusions evenly distributed on the leading edge of the blade.

[0043] Meshing strategies for fixed and rotated domains, such as Figure 4 As shown, the blade is divided into 100 nodes along the chord direction and 65 nodes along the height direction. To meet the analytical accuracy requirements for wall flow in the calculation, 65 boundary layer meshes are arranged on the blade surface, with the first layer mesh having a height of 2×10⁻⁶. -5 m, with a grid height growth ratio of 1.1.

[0044] The computational domain boundary conditions are set as follows: Figure 4 As shown, the fixed domain inlet is set as a velocity inlet with a velocity magnitude of 8 m / s and a turbulence intensity of 0.5%. The fixed domain outlet is set as a pressure outlet. The boundary condition of the interface connecting the fixed domain and the rotating domain is set as Interface. The blades and rotating shaft in the rotating domain are set as Wall boundary conditions. The boundary conditions of the other surfaces are set as Symmetry. The sliding mesh method is used to simulate the rotation of the blades of the vertical axis wind turbine. The blade tip speed ratio is defined as Equation (5). The blade rotation angular velocity ω is set as 12 rad / s (TSR = 1.5), 17.52 rad / s (TSR = 2.19), and 24 rad / s (TSR = 3) under different blade tip speed ratios.

[0045]

[0046] Among them, when the tip speed ratio is 2.19, the monitoring results of the power coefficient of the vertical axis wind turbine are as follows: Figure 5 As shown, the power coefficient fluctuates greatly in the first three blade rotations. To avoid the influence of non-convergence on the conclusions, the data from the 16th rotation is used uniformly for analysis. Figure 5 The results show that choosing a time step of 1° ensures the accuracy of the analysis.

[0047] To ensure computational accuracy, three computational grids were used for grid independence verification. The outer domain used a grid with 2.2 million nodes, and the grid refinement strategy in the rotation domain was as follows: Figure 6As shown, the mesh densities of the internal rotating domain are coarse, medium, and fine, with 2 million, 3.7 million, and 5.2 million meshes respectively. The total number of meshes calculated for the three groups are 4.2 million, 5.9 million, and 7.4 million respectively. The performance deviation of the coarse mesh is caused by insufficient mesh nodes when the blade is located in the downstream region. Comparing the calculation results of the medium-density mesh and the fine-density mesh, it is found that their changing trends are basically the same. Therefore, 5.9 million mesh nodes are selected as the calculation mesh.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for building a model of a biomimetic vertical axis wind turbine, characterized in that, The specific steps include: Step 1, selecting NACA0021 airfoil as the blade profile; The blade chord length of the blade profile is c = 0.265m, the blade height is H = 1.2m, and the rotation radius of the blade is R = 1m; Step 2, the shape of the protrusion at the leading edge of the fan blade is a sinusoidal curve, and the protrusion cross-sectional profile is obtained by transformation of the basic airfoil; The transformation mode of the protrusion cross-sectional profile is: （1）， In equation (1), (x, y) is the coordinate of the maximum thickness point of the airfoil, x k , y k (x, y) is the coordinate of the maximum thickness point of the airfoil, A is the amplitude of the protrusion; Step 3, dividing the calculation domain into a fixed domain located outside and a rotating domain located inside; The rotating radius of the rotating domain is 1.2 R , the rotating domain height is the same as the blade height H , the radius of the semicircle at the left inlet of the fixed domain is 10 R , the distance between the fixed domain outlet and the rotating domain is 30 R , in order to consider the influence of the tip vortex generated in the study, the height of the calculation domain is greater than the height of the blade, which is set to 2 H ; Step 4, calculating the flow field of the wind turbine by using ANSYS Fluent software; Step 5, verifying the accuracy of the numerical simulation of the vertical axis wind turbine.

2. The method of claim 1, wherein, The turbulence model in step 4 adopts the widely used SST model in numerical simulation of vertical axis wind turbines k ω , the incompressible air is selected as the flow medium, the fluid density is set as 1.225 kg / m 3 , the time step of calculation is set as the time required for the blade to rotate 1°, 40 iterations are set in each time step, and the total physical time length is set as the time required for the blade to rotate 16 times.​ 3. The method of claim 1, wherein, In step 5, the time step, total physical time, grid density, and differences between simulation and test are verified, and the relationship between power coefficient, torque coefficient and tangential force coefficient is: （2）， （3）， （4）， in equations (2), (3), (4), C power is the power coefficient of the wind turbine, TSR is the tip speed ratio, Q is the torque of the wind turbine, ρ is the gas density, H is the height of the wind turbine blade, R is the radius of the blade rotation, U is the main flow velocity, C Q is the torque coefficient of the wind turbine, C T is the tangential force coefficient of the wind turbine, is the average chord length of the blade.

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